1. Field of Invention
This invention concerns a filament lamp and light irradiation type heat treatment apparatus, and particularly, a filament lamp used for heat treatment of an article and light irradiation type heat treatment apparatus equipped with such a filament lamp.
2. Description of Related Art
Heat treatment is used in a variety of processes in the manufacture of semiconductors, including film growth, oxidation, nitriding, film stabilization, silicidation, crystallization, and ion implantation activation. In particular, rapid thermal processing (hereafter, RTP) of a semiconductor wafer or other article to be treated by quickly raising and lowering its temperature enables improved step size and quality, and so its use is desirable. Incandescent lamps, for example, are used as the light source in this type of light irradiation type heat treatment apparatus (simply “heat treatment apparatus” hereafter).
Incandescent lamps have filaments arranged inside bulbs made of a material that is transparent to light; they irradiate 90% or more of the invested power, and can heat the article W to be treated without making contact. Therefore, it is possible, when using them as heat sources for heating glass substrates or semiconductor wafers, to raise the temperature of the article to be treated more quickly than by the resistance heating method, specifically, to a temperature of 1000° C. or higher in a period from several seconds to several tens of seconds, and also to cool the article quickly by stopping the light irradiation.
When using light irradiation type heat treatment apparatus of this type to perform RTP of semiconductor wafers, for example, unevenness of the temperature distribution of a semiconductor wafer when it is heated to a temperature of 1050° C. or higher is liable to cause a phenomenon called “slip” in the semiconductor wafer, in which crystal transition defects arise and quality declines, and so it becomes necessary to heat the semiconductor wafer, hold it at a high temperature, and then cool it so that the temperature distribution will be even across the entire surface. In other words, highly precise uniformity of temperature of the article to be treated is sought in RTP.
Even in the event that the light irradiation is performed so that the degree of irradiation is even for semiconductor wafers that have the same treatment characteristics across the entire irradiated surface, at the edges of the semiconductor wafer heat will be radiated by the side surfaces of the semiconductor wafer, and so the temperature at the edges of the semiconductor wafer will be reduced and there will be unevenness in the temperature distribution of the semiconductor wafer.
To resolve problems of this sort, there have been attempts to make up for the temperature drop due to heat radiation from the sides of the semiconductor wafer, and thus, even out the temperature distribution in the semiconductor wafer by means of light irradiation of the surface at the edges of the semiconductor wafer to a greater degree than the surface at the center of the semiconductor wafer.
In conventional heat treatment apparatus, an arrangement is known like that shown in FIG. 9, for example, in which multiple incandescent lamps 62, 63 are located above and below a chamber 61 made of a light-transparent material; those above and those below face each other and their axes cross. Both surfaces of the article to be treated that is accommodated within the chamber 61 are heated by means of light irradiation from the incandescent lamps 62, 63 (see, Japanese Pre-grant Patent Publication H7-37833 of 1995).
In this heat treatment apparatus, as shown in FIG. 10, in the upper stage the lamp output of the incandescent lamps L1, L2 at both ends is greater than the output of the lamp output of the incandescent lamp L3 in the middle, and in the lower stage the lamp output of the incandescent lamps L4, L5 at both ends is greater than the output of the lamp output of the incandescent lamp L6 in the middle. By this means, it is said, the temperature drop due to heat radiation at the periphery WB of the article W to be treated can be compensated; the temperature difference between the center and periphery of the article W to be treated can be reduced and the temperature distribution of the article W to be treated can be made uniform.
In the conventional heat treatment apparatus 60 described above, however, there may be small, narrow, special regions WA on the article W to be treated that are very small relative to the length of the emitted light of the incandescent lamp, as shown in FIG. 10, and when light irradiation is done at a light intensity appropriate to the characteristics of these special regions WA, the regions other than the special regions WA are irradiated under the same conditions, and so it has not been possible with earlier heat treatment apparatus to adjust temperatures to provide suitable temperature conditions for both the special regions WA and the other regions, or in other words, to control only the degree of irradiation of the small, special regions so that the temperature status of the article W to be treated will be even.
For example, it is common to form a film of metallic oxide or other material on the surface of a semiconductor wafer by the sputtering method and then to dope it with impurities by means of ion implantation; the film thickness of such a metallic oxide and the density of the impurity ions will have a localized distribution on the surface of the semiconductor wafer. This localized distribution will not necessarily have symmetry with respect to the center of the semiconductor wafer; sometimes, with regard to the density of the impurity ions, for example, the density of the impurity ions varies in small, special regions that do not have central symmetry with respect to the center of the semiconductor wafer.
Even in the event that light irradiation is performed so that there is the same degree of irradiation of such special regions and the other regions, there will be differences between them in the speed of temperature rise and the temperature in the special regions will not necessarily be the same as the temperature in other regions.
Accordingly, in the conventional heat treatment apparatus 60 described above, there may be the problem that an unwanted temperature distribution in the treatment temperature of the article W being treated results in difficulty in giving the desired physical properties to the article being treated.
In conventional heat treatment apparatus, an arrangement is also known like that of FIG. 11, for example, in which there is a first lamp unit 72 within a lamp housing 71 that comprises an array of multiple double-ended lamps 73 that are U-shaped so they are both parallel and perpendicular to the surface of the figure, with power supplies that feed the filaments 75 fitted in both ends of the bulbs, and below the first lamp unit 72 a second lamp unit 76 that comprises an array of multiple double-ended lamps 77 with a straight line shape running along the surface of the Figure and perpendicular to the surface of the figure, with power supplies that feed the filament attached to both ends of the bulbs. A semiconductor wafer or other article W to be treated placed on a support ring 78 that is positioned below the second lamp unit 76 and heated (see, Japanese Pre-grant Patent Publication 2002-203804).
In this heat treatment apparatus 70, in order to raise the temperature of the portion of the article W to be treated that is in contact with the support ring 78 on which the article W to be treated is placed, which tends to have a lower temperature than other portions, there is a mechanism to control the U-shaped tubes belonging to the first lamp unit 72 positioned over the contact portion, by increasing their power.
In this heat treatment apparatus 70, first the regions to be heated in the semiconductor wafer that is the article W to be treated are divided into multiple concentric zones with central symmetry, the light-irradiation distributions of the lamps to the first lamp unit 72 and the second lamp unit 76 are combined, a synthesized light-irradiation distribution pattern that has central symmetry with respect to the center of the semiconductor wafer corresponding to the zones into which the wafer is divided is formed, and in order to control the effect of scattering in the intensity of light from the lamps, the semiconductor wafer is rotated as heat treatment is applied in response to temperature changes in the individual zones.
It becomes possible, by means of this heat treatment apparatus 70 to individually heat the concentric zones on the article W to be treated and thereby, it was said, to make the temperature state of the article W to be treated uniform.
Nevertheless, in the event that the special regions mentioned above do not have central symmetry with respect to the center of the semiconductor wafer, it is not possible to solve the problem described above properly because heat treatment is done by rotating the semiconductor wafer.
Moreover, it is thought that the following problems could occur if this heat treatment apparatus 70 were actually used. Specifically, a U-shaped lamp comprises a horizontal portion 74B and a pair of vertical portions 74A, but because only the horizontal portion 74B where the filament 75 is located contributes to light emission, the individual lamps are separated by space to a degree that cannot be ignored, and so it is conceivable that temperature distributions will occur in areas beneath the spaces.
That is, even though the illumination-intensity distribution of the first lamp unit 72 is combined with that of the second lamp unit 76 to form a synthesized illumination intensity distribution with central symmetry on the semiconductor wafer, the illumination intensity beneath the spaces mentioned above will change (drop) rapidly, and so even though heating is performed in response to the temperature changes in each zone, it will conceivably be relatively difficult to reduce the temperature distribution that occurs in the vicinities beneath the spaces.
Furthermore, with regard to this sort of heat treatment apparatus 70, there has been a trend in recent years to reduce space (primarily in the height direction) for laying out the lamp units as much as possible, and so, if U-shaped lamps are used, space will be needed for the vertical portions of the lamps; this is not desirable from the perspective of space reduction.
In view of the above noted circumstances, the present inventors proposed a filament lamp, to be used as the light source of light irradiation type heat treatment apparatus with the following construction (see, Japanese Pre-grant Patent Publication 2006-279008). FIG. 12 is an explanatory perspective view that schematically shows the construction of one example of such a conventional filament lamp.
This filament lamp 80 has a straight-line bulb 81 that is hermetically sealed at both ends, and within the bulb 81 are multiple (two are shown in FIG. 12) filament assemblies 83A, 83B, comprising coiled filaments and leads that supply power to the filaments, that are sequentially arranged so that the filaments extend in the axial direction of the bulb 81.
In one filament assembly 83A, an end of a lead 86A that is connected to one end of the filament 84A is threaded through the through hole 92A formed in an insulator 91 made of quartz glass, for example, that is set between the filaments 84A, 84B and is electrically connected to an external lead 88A that projects outward from one hermetically sealed portion 82A by way of a metal foil 87A embedded within the hermetically sealed portion 82A at one end of the bulb 81A, and another lead 85A connected to the other end of the filament 84A in the filament assembly 83A is electrically connected to an external lead 88D by way of a metal foil 87D embedded within the hermetically sealed portion 82B at the other end of the bulb 81. There is an insulating tube 90B on the portion of the lead 85B that is opposite the filament 84A of the other filament assembly 83A.
A power supply 93A is connected to one filament assembly 83A by way of the external leads 88A, 88D, and another power supply 93B is connected to the other filament assembly 83B by way of the external leads 88B, 88C, by which means power can be supplied individually to the filaments 84A, 84B of the filament assemblies 83A, 84A.
Further, 89 is a circular anchor set along the axial direction of the bulb 81 in a position between the inner wall of the bulb 81 and the insulating tubes 90A, 90B; each filament 84A, 84B is supported by perhaps three anchors 89 so that it does not contact the bulb 89.
This filament lamp 80 has multiple filaments 84A, 84B within the bulb 81 and is constituted to provide individual control of the light emitted by each filament, so that if it is used as a light source for heating in light irradiation type heat treatment apparatus, it is possible to arrange filaments with higher precision with respect to the regions to be irradiated on the article to be treated that was possible using conventional filament lamps having a single filament in the bulb, by aligning the filaments in parallel rows.
Accordingly, by means of such light irradiation type heat treatment apparatus, it is possible to supply power individually to the multiple filaments 84A, 84B and to individually control the light emitted by each filament 84A, 84B. Thus, it is possible to irradiate with the desired irradiation distribution according to the characteristics of the article to be treated even when the distribution of localized temperature variations on the article to receive heat treatment is non-symmetrical with respect to the article to be treated. As a result, the article to be treated can be heated evenly and an even temperature distribution can be achieved across the entire irradiated surface of the article to be treated.
Furthermore, when compared with the heat treatment apparatus 70 that has U-shaped lamps described above, these filament lamps can have a straight-line shape and so do not require space corresponding to the vertical portion of U-shaped lamps. As a result, it is possible to reduce the size of the heat treatment apparatus.